Posftix, courier mysql Ubuntu no receive external mail

Hi!, I've been looking for this trouble in the forum but I did'nt found an answer to help me, and I need this to make it works.

Here is the thing, I've installed Postfix with courier and mysql.
I can create accounts and access through squirrelmail, I can send and receive mail from my own domain, I can also send mail to external server (like gmail, hotmail, outlook, etc... ) but when I receive an email from one of this accounts (ex: gmail) is reject.

I've already check mail.log and it doesn't show anything, there is no change in it. I also make a test with an online smtp test. And it shows: